Treatment of fibrous insulating materials



purpose.

the wire either in selected single colors or in Patented Apr. 11,

- UNITED STATES 2,346,324 TREATMENT OF FIBROUS INSULATING MATERIALSThomas E. ODonnell, Westfleld, N. 1.,

to Western Electric Company, Incorporated, New York, N. Y., acorporation of New York No Drawing. Application August 1:. 1941,

Serial No. 406,724

6 Claims.

This invention relates to the treatment of fibrous insulating materials,and more particularly to methods for treating fibrous materials for useas insulation on electrical conductors.

Electrlcalconductors employed in electrical apparatus, such ascommunication equipment, are often provided with fibrous insulation,such as silk or cotton, and the type of fibrous material used in eachinstance depends primarily upon service requirements and.costconsiderations. It is, of course, desirable to use the more plentifuland less expensive cotton wherever possible and a primary considerationwhich normally governs and restricts the use of cotton for this purposeis the fact that its electrical insulating characteristics tend to varywidely with service con- -(iltion s.- Ordinarily, cotton possessesfairly good insulating properties in a relatively dry state,

but its insulation resistance values are lowered substantially when thecotton is exposed to moist air. Consequently, it is desirable to improvethe insulation resistance of the cotton, particularly in the presence ofmoisture, in order to permit its use on conductors which encounter suchconditions in service.

In many cases it is desirable to provide insulated wires withsome'identifying marking and when fibrous insulation is used on thewires it is convenient to employ colored materials for this 'Ihe coloredmaterials are applied on color combinations as a means of identifyingin-. dividual wires in the, apparatus or circuits. in which they areeventually incorporated.

The present invention is particularly adapted to the production ofcotton in a variety of colors for use as insulation on electricalconductors that require high insulation resistance values over a widerange of operating conditions.

An object of this invention is the provision of improved methods fortreating fibrous materials, such as cotton in strand or textile form, toincorporate a durable and fast dye in the cotton and also improve theelectrical insulating char- .4

acterlstics of the cotton.

In accordance with one embodiment of the invention, fibrous material,such as cotton strand, is enclosedin a pressure chamber and a hotaniline dye liquor containing calcined gypsum in solution is circulatedunder pressure through the fibrous material for a predetermined period,after which the liquor is-drained from the pressure chamber and a diluteaqueous carbonic acid solution ,then circulated through the pressurechamber and the cotton for a definite time period.

The cotton may be then washed with clear water and thoroughly dried tocomplete the process.

The invention can be practiced conveniently in a conventional dyeingmachine, such .as the Franklin dyeing machine, the Thies dyeing machine"or the Obermaier dyeing machine,

all of which are well known and are employed generally for dyeingtextile materials. All of these machines operate on a similar principle10 and comprise a sealed pressure chamber which contains a plurality ofperforated hollow spindles which support the textileand which areconnected in a fluid supply system whereby fluids are fed underpressure, from a pump into the perforated spindles or into the pressurechamber adjacent to the spindles. The textile, usually strand woundsomewhat loosely into cylindrical packages, is mounted on eachperforated spindle. The pressure chamber is then sealed andthe fluidforced, under pressure from-the pump, through the perforated spindles,the textile and the pressure chamber, after which the fluid is returnedto, the pump and recirculated continuously as long as the process iscontinued.

'These machines are provided with a suitable system of piping'and valvesto permit circulating of the fluid through the cotton either outwardlyfrom the spindle or inwardly to the spindle. In the first instance,usually designated as circulating from inside to outside, the fluid fromthe pump is forced through the perforated spindle, through the textile,through the pressure cham- 'ber, and back to the pump in that order. Inthe second instance, which is termed circulation from outside to inside,the path of fiuid flow runs from the pump into the pressure chamber,through the textile, through the perforations in the hollow spindle. anddown through the spindle to a pipe running to the pump.

For the process of this invention, a number of the wound packages areinserted over each spindle of the above described apparatus and thepackages on each spindle are then clamped to- .gether in end to endengagement. The tubes have bevelled end portions and are longitudinal-1y compressible to a slight extent so that clamping the tubes on thespindle provides essentially tight Joints between successive packageswith the as quantity of dye of the desired color is first added to hotwater and stirred until the dye dissolves or forms a satisfactorysuspension. The prepared dye liquor is then placed in the apparatus andbrought to a. temperature of about 160 F., by either cooling or heatingas required, and circulation of the liquor through the cotton packages,as above described, is then started.

Shortly after circulation of the dye liquor is started, a quantity ofcalcined gypsum is added anddissolved or suspended in the liquor orsolution. The best grade of calcined gypsum is used for this purpose.

The quantity of calcined gypsum to be added at this stage of the processdepends upon the quantity of cotton being processed and a quantity ofcalcined ypsum equal to .25% of the total weight of the cotton inprocess, in the pressure chamber, is added to the liquor shortly aftercirculation of the liquor through the cotton is started. Circulation ofthe liquor, which is then at a temperature between 155 F. and 165 F.,preferably 160 F., is continued for about 15 minutes to provide a lowtemperature treating and dyeing period.' At the termration of this lowtemperature treating period, the temperature of the liquor, or treatingsolution, is raised gradually, conveniently by introducing live steamthereto, until it attains a temperature between 195 F. and 205 F.,preferably 200 F. Circulation of the treating solution through thecotton is continued during this heating period and the addition of heatis controlled so that about 15 minutes, equal to the low temperaturetreating period, is required for the specified temperature rise. Afterthe liquor reaches a temperature of 195-205 F., it is maintained at thattemperature, by introduction of steam for example, and circulation ofthe solution through the cotton continued at that temperaturefor aboutone-half hour, or about twice the low temperature treating period. Theexact durations of these temperature periods may vary from the givenvalues but they should be coordinated and the above ratios .should bemaintained with the low temperature and the heating periods of equallength and the high temperature treating period being twice the lengthof the low temperature treating period.

As stated above, the amount of calcined yp um added to the liquor nearthe beginning of the process depends upon the quantity of cotton inprocess, and a unit quantity equal to .25% of the cotton weight is addedat that time. The total quantity of gypsum to be added during thecomplete process depends also upon the color of the dye being applied tothe cotton. For certain colors, such as yellow and blue, no furtheradditions of calcined gypsum are needed after the first addition is madenear the start of the process and the unit" quantity added at'that timeis adequate. For other colors, however, further additions of calcinedgypsum are needed as the process progresses. For such colors as black,

brown, green, orange and red, three further additions of calcinedgypsum, each equal to the unit quantity, or .25% of the cotton weight,are made during the operation, making a total of four additions. Theseunit quantities are added at uniform intervals, or roughly at the end ofeach 15 minute period. Thus, the first addition is made near thebeginning of the process with the liquor at about 160 F., the second ismade approximately 15 minutes later when heating of the solution toincrease its temperature begins, the third addition is made at about thetime the solution attains its maximum temperature, and the finaladdition is made at about the mid-point of circulation at the maximumtemperature, or the high temperature treating period. Although no closecoordination between the total volume of solution and amount of gypsumis required, the total quantity of gypsum added in four unit quantities,equal to 1% of the-cotton weight, will saturate the volume of liquorused with the corresponding weight of cotton.

During this operation, the direction of flow of the treating solution isreversed periodically, by proper regulation of the valves, to force theliquor successively from the inside to the outside of the cottonpackages and from the outside to length of time, the pump is stopped andthe liquor is removed from the pressure chamber. The cotton is thenwashed or flushed with clear water heated to a temperature of about 140F. and in this operation the clear water is circulated through theapparatus and forced through the packages in the same manner employedfor circulation of the treating solution.

In the next step in the process, the cotton is treated with a purifyingliquid or solution which may be prepared by dissolving carbon dioxidegas in water to form a dilute aqueous solution of carbonic acid having apH from 4 to 5. The usually available tap water is suitable for thispurpose and the carbon dioxide gas is introduced to the water undersuitable pressure to cause the necessary quantity of gas to dissolve andremain dissolved in the water.

The pH of tap water varies somewhat, depending mainly upon the watersource and in some cases treating processes that are applied to thewater supply, but most commonly available waters can be used forpreparation of the purifying liquid by dissolving in the water asufiicient quantity of carbon dioxide gas to provide a solution havingthe desired pH value.- Best results are obtained when the purificationliquid, or agent, has apH 01' 4.5 and this exact value is usedpreferably, though the pH of the agent can vary between the limits of 4and 5. For different tap waters, I different additions of CO2 are, 01'course, required to produce the desired pH- values but after thequantity of carbon dioxide required per unit volume of any particulartap water has once been established, it is convenient to prepare thepurifying liquid in any desired quantities by merely combining thecomponents in the established proportions.

The aqueous solution of carbonic acid is prepared in a suitablecontainer and then introduced to the apparatus, wherein it is circulatedthrough the pressure chamber and the cotton packages, as abovedescribed. During preparation of the solution, during any necessarystorage period and while the solution is in the apparatus, it ismaintained constantly under a suitable pressure to prevent escape of thecarbon dioxide from the process. Circulation of the purifying solutionis continued, with periodic reversals of circulation direction, forabout one hour.

After completion of the washing operation, the cotton-may be flushedwith clear water, after which it is removed from the apparatus,thoroughly dried and is then ready for subsequent operations.

The resultant product exhibits electrical insulating properties whichare greatly superior to those possessed by ordinary cotton. Thisimprovement is due partly to the removal from the cotton of certainionizable impurities or electrolytes, such as compounds of the alkalimetals, which occur naturally in cotton. The successive application tothe cotton of the calcined gypsum and the carbonic acid solutionseffectively removes these ionizable impurities and otherwise improvesthe electrical insulating properties of the cotton.

The manner in which these agents perform their respective and combinedfunctions is not clearly understood. However, it appears that the cottonfibres have a high aifinity for the calcium cations present in thecalcined gypsum solution and that the gypsum is carried into the fibresto replace portions of the more readily soluble and ionizable impuritiesfound naturally in the cotton. The subsequent introduction of thecarbonic acid solution accomplishes a further removal bf these ionizableimpurities from the cotton and apparently also aflects the condition ofthe calcium deposits in the fibres with the re-- sult that they areirreversibly adsorbed by the fibres. Whatever the exact action of theseagents may be, their use in accordance with this process results masuificient improvement in the electrical insulating properties of thecotton to permit its adoption in many electrical circuits and apparatus.

The use of calcined gypsum in the dye liquor also improves the dyeingaction and the condition of the dye deposit. As stated above, the cottonis supported in rigid packages on rigid perature approximately 160 F.and containing tubes in the processing apparatus. The addition of thecalcined gypsum to the dye liquor, and the coordinated temperaturecycles above described, assist the depositing of the dye in the cotton.The dye deposit in the cotton fibres is fast and durable and noappreciable bleeding of the dye occurs during the subsequent treatmentwith the carbonic acid solution and final washing with water.

Although the processes herein described are particularly adaptable fortreating cotton in the form of strands wound into packages, the processis also suitable for treating fibrous materials in other forms, such aswoven fabric. apparent that other adaptations and modifications of theprocess are feasible and it is to be understood that the invention islimited only by the scope of the appended claims.

What is claimed is:

1. In a method of preparing cotton for use as electrical insulation, thesteps of treating the cotton with a water solution of dye heated to atemperature between 155 F. and 165 F. and containing a unit quantity ofcalcined gypsum for an initial treating period of predetermined length,then adding a second unit quantity of calcined gypsum equal to saidfirst unit quantity i will be a unit quantity of calcined gypsumdissolved 'therein for a low temperature treating period ofpredetermined length, then adding a unit quantity of calcined gypsum tothe liquor and simultaneously adding heat to the liquor to increase itstemperature to about 200 F., adding another unit quantity of calcinedgypsum to the liquor at the time the liquor attains a temperature ofabout 200 F., maintaining the liquor at a temperature of about 200 F.and treating the cotton therewith for a high temperature treating periodof twice the length of the low temperature heating period, addinganother unit quantity of calcined gypsum to the liquor at about themid-point of said high temperature heating period, and finally treatingthe cotton mass with an aqueous solution of carbonic acid.

3. In a method of preparing cotton for use as electrical insulation, thesteps of enclosing a mass of the cotton in a pressure chamber, forcing awater solution of dye heated to a temperature between F. and 155 F. andcontaining a unit quantity of calcined gypsum equal to approximately 25%of the weight of the cotton mass through the chamber and the cotton massfor a low temperature treating period of predetermined length, adding asecond unit quantity of calcined gypsum to the treating solution andsimultaneously adding heat to the solution to raise its temperature to195 F.-205 F., adding a third unit quantity of calcined gyp um to thesolution at the time the solution attains the higher temperature,maintaining the solution at the higher temperature range and forcing thesolution through the chamber and cotton for a high temperature treatingperiod .of substantially twice the length of the 10w temperaturetreating period, adding a fourth unit quantity of calcined gypsum to thesolution at about the mid-point of said high temperature treatingperiod, and finally forcing an aqueous solution-of carbonic acid throughthe chamber and cotton mass.

4. In a method of preparing cotton for use as electrical insulation, thesteps of enclosing a mass of the cotton in a pressure chamber, forcing awater solution of dye heated to a temperature between 155 F. and F. andcontaining a unit quantity of calcined gypsum on the order v of 25% ofthe weight of the cotton mass through the chamber and the cotton massfor a low temperature treating period of definite length, then adding aunit quantity of calcined gypsum to the solution and simultaneouslyadding heat to the solution, said heat being added at a suitable rate tocause the solution to attain a temperature. between 'F. and 205 F. in alength of time equal to about the length of the low temperature treatingperiod, while the solution is being forced through the cotton mass,adding a unit quantity of calcined gypsum to the solution at the timethe solution attains. the higher temperature,

ture range and forcing the solution through the cotton mass for a hightemperature treating period of twice the length of the low temperaturetreating period, adding a unit quantity of calcined gypsum to thesolution at about the mid-point of the high temperature treating period,and subsequently forcing through the chamber and the cotton mass anaqueous solution of carbonic acid.

5. In a method of preparing cotton for use as electrical insulation, thesteps of enclosing a measured mass of the cotton in a pressure chamber,forcing a water solution of dye heated to a temperature around 160 F.and containing a unit quantity of calcined gypsum equal to substantially25% of the cotton mass weight through the chamber and the cotton massfor an initial treating period, then at the end of the initial treatingperiod adding a unit quantity of calcined gypsum to the solution andsimultaneously adding heat to the solution at a suitable rate to causethe solution to attain a temperature around 200 F. in a length of timeequal to the initial treating period while the solution is being forcedthrough the cotton mass, adding a unit quantity of calcined gypsum tothe solution as soon as it attains the higher temperature, maintainingthe treating solution at the higher temperature and forcing it throughthe cotton mass for a period of time equal to twice the length of theinitial treating period, adding a unit quantity of calcined gypsum tothe solution at about the mid-point of the period during which thesolution is maintained at the higher temperature, and finally forcingthrough the cotton mass an aqueous solution of carbonic acid.

6. In a method of preparing cotton for use as electrical insulation, thesteps of enclosing a mass of the cotton in a pressure chamber, initiallytreating the cotton for a period of about 15 minutes with a dye liquorheated to a temperature around 165 F. and containing a unit quantity ofcalcined gypsum equal to approximately 25% of the weight of the cottonmass, then adding a unit quantity of calcined gypsum to the liquor andsimultaneously adding heat to the liquor to cause the liquor to attain atemperature between 195 F. and 205 F. in a period of about 15 minuteswhile treatment of the cotton with the liquor is continued, adding aunit quantity of calcined gypsum to the liquor at the time the liquorattains a temperature between 195? F. and 205 F., treating the cottonwith the liquor at the higher temperature for a period of about 30minutes and adding a unit quantity of calcined gypsum to the liquor atabout the mid-point of said 30 minute period, and finally forcingthrough the cotton mass an aqueous solution of carbonic acid having a pHbetween 4 and 5.

THOMAS E. O'DONNELL.

